Robotic surgical systems have been used in minimally invasive medical procedures in which surgical instruments were inserted through surgical portals at fixed entry points into the patient's body. These systems incorporated a Remote Center of Motion (RCM) to ensure that the surgical instruments did not move beyond these fixed entry points as the instruments were manipulated inside the patient's body. Many of these surgical robots used a mechanical RCM with a portion of robotic arm attaching directly to the surgical portal. Unlike surgical robots using mechanical RCM's, software-based RCM's typically did not mechanically connect to the surgical portal in order to provide an increased range of motion and reduce collisions between robotic arms of the surgical robot. Unfortunately, many of the surgical robots with software-based RCM's tend to complicate instrument exchanges as the surgical portals moved out of alignment with the robotic arms when the surgical instruments were removed.
During an instrument exchange, the surgical instrument was pulled out of the surgical port and removed from the robotic arm. A new or different surgical instrument was then connected to the robotic arm and introduced back through the surgical portal. Surgical robots with mechanical based RCM's facilitated the exchange because the surgical portal was continually held in alignment with the linear axis of the instrument motion by a linkage or connection to the surgical portal. In contrast, surgical robots with software-based RCM's did not have a connection or linkage to the surgical portal and therefore lost alignment when the surgical instrument was removed from the surgical portal. Inserting another surgical instrument required the clinician to manually align the surgical portal with the surgical instrument. This process increased the time required for conducting the instrument exchange.
Accordingly, there is a need for robotic surgical systems with software-based RCM's that facilitate instrument exchange by maintaining alignment of the surgical portal and robotic arm.